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  Medical devices with variable stiffnessUSPTO Application #: 20070043306Title: Medical devices with variable stiffness Abstract: Medical devices capable of having variable stiffness, and related methods, are disclosed. In some embodiments, a medical device includes an elongated member adapted to be inserted into a subject, and an electrorheological fluid carried by the elongated member. (end of abstract) Agent: Fish & Richardson PC - Minneapolis, MN, US Inventor: Greg Olson USPTO Applicaton #: 20070043306 - Class: 600585000 (USPTO) Related Patent Categories: Surgery, Diagnostic Testing, Flexible Catheter Guide The Patent Description & Claims data below is from USPTO Patent Application 20070043306. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The invention relates to medical devices, such as, for example, catheters, guide wires, and medical tubing. BACKGROUND [0002] Intravascular medical devices such as, for example, guidewires, catheters, and medical tubing, allow physicians to perform a medical procedure. As an example, a balloon catheter can be used to administer a variety of treatments. In an angioplasty procedure, the balloon catheter can be used to widen a constricted bodily vessel, such as a coronary artery. The balloon catheter can also be used to deliver a tubular member, such as a stent, that is placed in the body to reinforce or to reopen a blocked vessel. [0003] In angioplasty, a balloon can be used to treat a stenosis, or a narrowing of the bodily vessel, by collapsing the balloon and delivering it to a region of the vessel that has been narrowed to such a degree that blood flow is restricted. The balloon catheter is passed over an emplaced guidewire that is inserted into a patient's vascular system at a convenient site, and subsequently delivered, e.g., pushed, through the vascular system to a target site. Upon reaching the site, the balloon is then expanded, e.g., by injecting a fluid into the interior of the balloon. Expanding the balloon can expand the stenosis radially so that the vessel can permit an acceptable rate of blood flow. After use, the balloon is collapsed and withdrawn. [0004] In stent delivery, a stent is compacted on the balloon and transported to a target site. Upon reaching the site, the balloon can be expanded to deform and to fix the stent at a predetermined position, e.g., in contact with the vessel wall. The balloon can then be collapsed and withdrawn. [0005] In some cases, the path that the device takes through the vascular system to the target site can be relatively tortuous, for example, requiring the device to change direction frequently. It is desirable for the medical device to have relatively good trackability so that it can travel along the tortuous path. At the same time, the device preferably has good pushability so that forces applied at the proximal end of the device can be transmitted distally to deliver the device. SUMMARY [0006] The invention relates to medical devices having selectively variable stiffness. [0007] In one aspect, the invention features a medical device, including an elongated member adapted to be inserted into a subject, and an electrorheological fluid carried by the elongated member. [0008] The electrorheological fluid is capable of providing the medical device with adaptable stiffness. By application of an electric field, the electrorheological fluid is capable of reversibly transitioning between a liquid-like state and a gel-like or solid-like state, thereby changing its stiffness and the stiffness of the medical device in which the electrorheological fluid is used. At a proximal portion, for example, the electrorheological fluid can enhance the pushability of the medical device, and a distal portion, the electrorheological fluid can enhance the flexibility and trackability of the device. The stiffness of the electrorheological fluid can be controlled by controlling the application of the electric field. [0009] In another aspect, the invention features a medical device, including an elongated member adapted to be inserted into a subject, and an electrorheological fluid carried by the elongated member. [0010] Embodiments may include one or more of the following features. The electrorheological fluid includes particles in a liquid. The particles include a composite having at least two different compositions. The particles include a first composition, and a second composition coating the first composition. The particles include a material selected from the group consisting of urea, butyramide, and acetamide. The liquid includes an oil. The elongated member includes a lumen, and the electrorheological fluid is in the lumen. The electrorheological fluid is on an exterior surface of the elongated member. The device is configured to apply an electric field to the electrorheological fluid. The elongated member includes two conductive members, the electrorheological fluid being between the two conductive members. The device includes a first portion having a first volumetric concentration of the electrorheological fluid, and a second portion having a second volumetric concentration of the electrorheological fluid different than the first volumetric concentration. The device includes a first portion having a first electrorheological fluid, and a second portion having a second electrorheological fluid different than the first electrorheological fluid. The device is catheter, such as a balloon catheter or a stent delivery catheter. The device is guidewire. The device includes multiple, independently-addressable portions of electrorheological fluid. The electrorheological fluid is contained in a receptacle. [0011] In another aspect, the invention features a method, including providing a medical device having an elongated member and an electrorheological fluid carried by the elongated member, applying an electric field to the electrorheological fluid, and changing the rheological properties of the electrorheological fluid. [0012] Embodiments may include one or more of the following features. The electric field is applied between two conductive members. The method includes applying different electric fields to the electrorheological fluid. The method includes applying a first electric field to a first electrorheological fluid, and applying a second electric field different from the first electric field to a second electrorheological fluid. The first and second electrorheological fluids have the different compositions. The first and second electrorheological fluids have different volumetric concentrations relative to the elongated member. The electrorheological fluid includes particles in a liquid. The particles include a composite having at least two different compositions. The particles include a first composition, and a second composition coating the first composition. The elongated member includes a lumen, and the electrorheological fluid is in the lumen. The electrorheological fluid is on an exterior surface of the elongated member. The medical device is tube, a balloon catheter, a stent delivery catheter, or a guidewire. [0013] In another aspect, the invention features a method of selectively changing the stiffness of one or more predetermined portions of a medical device. The method includes applying an electric field to the medical device. [0014] Other aspects, features and advantages will be apparent from the description of the preferred embodiments thereof and from the claims. DESCRIPTION OF DRAWINGS [0015] FIG. 1A is a cross-sectional view of an embodiment of an over-the-wire balloon catheter; and FIG. 1B is a cross section of the balloon catheter of FIG. 1A, taken long line 1B-1B. [0016] FIG. 2 is a cross-sectional view of an embodiment of an over-the-wire balloon catheter. [0017] FIG. 3 is a cross-sectional view of an embodiment of a rapid-exchange balloon catheter. [0018] FIG. 4A is a cross-sectional view of an embodiment of an over-the-wire balloon catheter; and FIG. 4B is a cross section of the balloon catheter of FIG. 4A, taken along line 4B-4B. [0019] FIG. 5 is a cross-sectional view of an embodiment of a guidewire. [0020] FIG. 6 is a cross-sectional view of an embodiment of a guidewire. Continue reading... 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